Process for depolymerizing dicyclopentadiene or its methyl homologues



Se t. 5, 1967 A. RENNER 1 3,340,315

PROCESS FOR DEPOLYMERIZING DICYCLOPENTADIENE OR ITS METHYL HOMOLOGUES Filed NOV. 4, 1964 x x Mia- HIII United States Patent 3,340,315 PROCESS FOR DEPOLYMERIZING DICY- CLOPENTADIENE OR ITS METHYL HOMOLOGUES Alfred Renner, Allschwil, Switzerland, assignor to Ciba Limited, Basel, Switzerland, a Swiss company Filed Nov. 4, 1964, Ser. No. 408,824 Claims priority, application Switzerland, Nov. 12, 1963, 13,872/ 63 1 Claim. (Cl. 260-666) It is known to manufacture cyclopentadiene on a large industrial scale by thermal depolymerisation. Inter alia, it has been proposed to depolymerise dicyclopentadiene in the liquid phase by subjecting a liquid batch of dicyclopentadiene to a decomposing distillation. However, the yield of monomer achieved in .this manner is relatively low because, owing to the long time of residence of dicyclopentadiene in the reaction zone, substantial amounts of higher polymers, such as tri-, tetraand penta-cyclopentadiene, form which, in contradistinction to dicyclopentadiene, cannot be split under the process conditions to furnish the monomer.

To overcome this disadvantage it was proposed in British Patent No. 612,893 to British Celanese Limited, Spondon, Great Britain, accepted Nov. 18, 1948, to depolymen'se dicyclopentadiene by heating it in a liquid auxiliary, for example in a hydrocarbon fraction boiling within the range from 190 to 250 C. But the yield claimed for this process is only 70% of monomer, referred to the starting material, consisting predominantly of dicyclopentadiene. To raise the yield of monomer, British Patent No. 769,813 to Chemische Werke Huls Aktiengesellschaft, Marl, Germany, published Mar. 13, 1957; and U.S. Patent No. 2,831,904 granted Apr. 22, 1958, to Robert W. F. Kreps, further proposed to introduce dicyclopentadiene in a liquid auxiliary boiling at 250 to 350 C., such as diphenyl ether, or into a hydrocarbon fr action boiling within this range, with the proviso that the speed at which the dicyclopentadiene is introduced is approximately equal to that at which the cyclopentadiene formed passes over. To ensure this and thereby to prevent the formation of a substantial share of higher polymers of cyclopentadiene, the concentration of monocyclopentadiene+dicyc1opentadiene in the liquid auxiliary must in general be kept below 5%. The yields of monomer obtained in this manner are stated to be about 96% to about 99% referred to the dimer. The low limit concentration of 5% of monocyclopentadiene +dicyclopentadiene considerably restricts the efliciency of this method. For the production of large amounts of monomeric C or c -cyclodienes very large amounts of liquid auxiliaries (2.5 to 8 times the amount of hourly production) must be circulated and regenerated.

In U.S. Patent No. 3,016,410 granted Jan. 9, 1962, to Clarence R. Dick et al., it has further been proposed to crack dicyclopentadiene in its dilute mixtures with low-boiling hydrocarbons, such as result as distillate fractions in the petroleum and coal tar industries, on the surface of a heating element to form monomeric cyclopentadiene. While this process gives an almost quantitative yield, it is unsuitable for cracking fractions having a high content of dicyclopentadiene or consisting of approximately pure dicyclopentadiene, because, owing to the absence of low-boiling petroleum fractions, the heating element would cause the heating of the whole reactor content up to the decomposition temperature of dicyclopentadiene. This would encumber ,the process with just those disadvantages which are found with the decomposition distillation of dicyclopentadieneinthe liquid phase which suffers from v ry pooryields and is bus -in sttial x l italilfiiatdifis y,ti h p wss i tl the :1

3,340,315 Patented Sept. 5, 1967 "ice U.S. patents is practically applicable only to mixtures containing less than 30% of dicyclopentadiene.

Since for the reasons described above the cracking of dicyclopentadiene in the liquid phase does not give entirely satisfactory yields on an industrial scale, the conventional large-scale processes are performed thus: First, dicyclopentadiene is vaporised and the vapours are conveyed through a hot reactor, for example a tubular reactor, whereby dicyclopentadiene is depolymerised to monocyclopentadiene. Since this depolymerisation is reversible at low temperatures, the problem facing industry is to fractionate and condense the cyclopentadiene vapours While preventing the partial reconversion of cyclopentadiene to dicyclopentadiene during the requisite cooling operation.

For the practical solution of this problem very complicated and expensive separating plants have so far been used, such, for example, as those described in U.S. Patent No. 2,801,270 granted July 30, 1957, to Joseph F. Nelson et al. and No. 2,913,504 granted Nov. 17, 1959, to George Oliver Hillard, Jr. et al.

However, the processes described in the above-mentioned patents aim primarily at using the depolymerisation of dimeric C and C -cyclodienes and mixtures thereof for their isolation from hydrocarbon mixtures or mineral oil fractions containing them. Therefore, several isolating operations are required, inter alia for example, the separation of higher-boiling accompanying substances, the separation of the C -cyclodienes from the C -cyclodienes and the removal of auxiliaries.

For converting strongly enriched dicyclopentadiene (over into the monomer the hitherto known processes, in which the depolymerisation of dicyclopentadiene is performed in the gas phase, are, however, not particularly suitable.

Thus, the process of U.S. Patent No. 2,801,270 granted July 30, 1957, to Joseph F. Nelson et a1. requires a high recirculation rate. According to column 3, line 30 of this patent this rate is equal to 50% to 250% of the initial batch. On one hand, this has the disadvantage that the capacity of the plant is reduced by the high recirculation rate. Moreover, this requires the repeated conveyance of substantial amounts of the material through the hot zones of the evaporator, of the reactor and of the column. One disadvantageous result of this is the formation of charred products which stop up the reactor after short working runs. Accordingly, the possible production runs are short and are only about 15 to 20 hours.

The process of U.S. Patent No. 2,913,504 granted Nov. 17, 1959, to George Oliver Hillard, Jr., et al. attempts to overcome this last-mentioned disadvantage by carrying out the depolymerisation in the reactor at a relatively low temperature or below about 300 C. respectively. While in actual fact this does considerably prevent the clogging of the plant and working runs of over 500 hours can be reached, this can only be achieved when a considerably reduced yield is accepted; it is only 30 to 70% of monomer, referred to the starting dimer.

For the consumer of cyclopentadiene, who buys the highly concentrated dicyclopentadiene from the petroleum or coal tar industries and converts it into the unstable cyclopentadiene for synthesis purposes, there still remained the unsolved problem of carrying out the depolymerisation of dicyclopentadiene to cyclopentadiene with simple plant to obtain a high yield and a high output per hour.

The present process offers for the first time a solution to this problem: Dicyclopentadiene is cracked in the gas phase in the known manner, the cracked gas is mixed with vapours of an inert liquid boiling above C., and

theresulting vapour mixture is conveyed into the bottom portion of a fractionating column. In this manner constantly high, substantially quantitative yields of cyclopentadiene are obtained over long working runs, and at the same time the undesirable necessity of recirculating large amounts of the batch is cut out.

Accordingly, the present invention provides a process for depolymerising the dimers of cyclopentadiene or of a methyl homologue thereof, wherein the dimer is cracked by heating in the gas phase in a reactor at least partially to the monomer; the monomer vapours are mixed with the vapours of a liquid boiling from 160 to 360 C. which does not decompose at this temperature and is inert towards the monomeric or dimeric form of cyclopentadiene and its methyl homologues; the resulting vapour mixture is conveyed into a fractionating column, and the pure monomer is withdrawn as a distillate at the head of the column.

In the present process it is advantageous to feed the dimeric cyclodiene into the reactor at the same rate as the monomeric cyclodiene is withdrawn at the head of the column; this is advantageously achieved by means of a device which, on one hand, when the boiling point of pure monomeric cyclodiene is exceeded, sets up a total reflux within the column and at the same time cuts off the supply of the dimer to the reactor, and on the other hand, reinstates the supply of the dimer and the withdrawal of distillate as soon as the boiling temperature of pure, monomeric cyclodiene has been reestablished at the head of the column.

Particularly long working runs can also be achieved by injecting the dimer into the upper end of a vertical tubular reactor heated at 200 to 400 0., this upper end being packed with filler bodies from copper metal or an alloy rich in copper, on which packing cyclopentadiene can evaporate.

Starting materials suitable for use in the present process are, for example, highly concentrated commercial dicyclopentadiene, highly concentrated commercial mixtures of isomeric bis (methylcyclopentadienes), and highly concentrated commercial mixtures of dicyclopentadiene and bis(methylcyclopentadienes). Such highly concentrated starting materials should in general contain at least 90% by weight of dimeric cyclodienes.

As a liquid which boils between 160 and 360 C. and is inert towards cyclopentadiene and dicyclopentadiene there may be used, for example, tetrahydronaphthalene (Tetralin), decahydronaphthalene (Decalin), a diethylbenzene, a dichlorobenzene or trichlorobenzene or a mixture thereof, or diphenyl ether. A petroleum fraction boiling above 200 C.-for example Shellsol R (registered trademark of Shell)may likewise be used.

The accompanying diagram illustrates a preferred variant of the process. From the storage tank 1 the starting material is conveyed through pipe 2 by pump 3 and calibrated. It is injected at the upper end of the vertical reactor 4, and drops on to the copper chip packing 5, where it vaporises. The reactor 4 is heated by three independent electric heating coils (not shown in the drawing), one in the upper third, one in the centre and one in the lower third. These three heating coils are governed by the thermometers 14, and 16. The gaseous reaction product is conveyed by the vapours of the liquid auxiliary rising out of the still 6 into the fractionating column 7. 12 represents a heating bath for heating the liquid auxiliary. At the thermometers 17 and 18 the bath temperature, and, respectively, the boiling temperatures of the liquid auxiliary are checked. 21 is a discharge valve associated with the still. On the column head there is provided a magnetic reflux divider 8 with a contact thermometer 19, by means of which the boiling temperature of the monocyclodiene concerned is adjusted. This contact thermometer controls the reflux divider 8 and the pump 3 in the following manner:

(a) When the temperature of the vapour phase at 8 is equal to the boiling temperature of the monocyclodiene or if it is lower, the pump 3 operates and all condensate formed in the condenser 9 is diverted through the condenser 10 to the receptacle 11, which is cooled by means of the cooling bath 13.

(b) As soon as the temperature of the vapour phase at 8 exceeds the boiling point of the monocyclodiene, the contact thermometer puts the pump 3 out of action (by means of relay not shown in the drawing) and switches the reflux divider over to total reflux. This state persists until the boiling temperature of the pure monocyclodiene has been reestablished at the column head. At this moment, phase (a) is reinstated dimeric cyclodiene is injected and monocyclodiene is withdrawn.

Examples 1 to 11 Commercial dicyclopentadiene was freed azeotropically from its water content before it was used. According to its gas chromatographic analysis it contained 93.9% of dicyclopentadiene.

The depolymeris-ation was performed in the apparatus described above under the following operating condit1ons:

The still 6 was charged with 250 ml. of tetrahydronaphthalene (boiling at 207 C.) which was heated to a vigorous boil. The boiling temperature of monocyclopentadiene (42 C.) was adjusted on the contact thermometer 19.

The reactor 4 used was a vertically disposed stainless steel tube of 35 mm. inside diameter and 600 mm. length. The fractionating column 7 used consisted of glass and had an inside diameter of 48 mm. and a height of 500 mm. The packing consisted of 4 mm. rings of wire netting.

Dicyclopentadiene was injected at the top end of the reactor. In the experiments listed in the following table, which lasted for 8 hours each, the output of the pump 3 and the temperature of the reactor were varied.

The following table shows the resulting outputs per hour and the yields achieved. The output -per hour is referred to the distillate in each case and the yields are the amount of distillate, referred to the amount of commercial dicyclopentadiene used.

TABLE Pump Reaction temperature 11313. ouitrput lzi'odlirc- Yield in on n ercent ml./I.nin. Top, Centre, Bottom, g./hour p A continuous run experiment was carried outunder the conditions of Example 9. The plant was operated for 280 hours without trouble and gave a constant yield of 98.5%; after this period some charred residues had to be removed from the top of reactor 4. Every time after 11 to 12 kg. of monocyclopentadiene had been withdrawn, the still 6 was emptied and recharged with 250 ml. of fresh tetrahydronaphthalene. When the exhausted content of the still is distilled, tetrahydronaphthalene can be recovered from it.

The water-clear distillate obtained in this experiment displayed the following analytical data: Boiling point: 42 C. n =l.4452.

GAS CHROMATOGRAPHIC ANALYSIS Example 12 Commercial dimeric methylcyclopentadiene is depolymerised in the same apparatus as used for Examples 1 to 11. The gas chromatogram of this starting material reveals the following composition:

The experiment was conducted under the following conditions (the figures in parentheses refer to the apparatus components shown in the drawing):

Pump output (3) ml./hr 720 Average temperature at top of reactor (14) C 145 Average temperature at center of reactor (15) C 290 Average temperature at bottom of reactor (16) C 340 Average oilbath temperature (12) C 215 Average still temperature (6) C 200 Temperature at head of column C 72 Bath temperature (13) C 0 Reflux ration within column (7) 1:1.6 Total amount of commercial dimethyldicyclopentadiene used kg 135.17 Duration of experimental run hrs 325 Amount of dimethyldicyclopentadiene used per hour g. 416 Total yield of monomeric methylcyclopentadiene kg 131.22 Production g /h r 404 The yield of distillate amounted to 97% referred to the amount of commercial dimethyldicyclopentadiene used.

The gas chromatogram of the distillate revealed the following composition:

The experiment was run for 3 Weeks, each Week rrom Monday morning till Friday night. During the weekends the experiment was discontinued and the apparatus was allowed to cool but was not cleaned. In all, the sump of the still 6 had to be renewed four times, using up a total of 1 kg. of Tetralin.

On completion of the test runi.e. after a working period of 325 hoursthe upper part of the reactor 4 was found to be stopped up by charred residues. When it was cleaned, g. of charred residues were removed from it.

What is claimed is:

A process for depolymerising dimers of a dicyclodiene selected from the group consisting of dimeric cyclopentadiene and dimeric methyl cyclopentadiene, wherein the dicyclodiene is cracked by heating in the gas phase in a reactor, to yield at least a preponderant share of the monomer; the dimer being injected into the top end of a vertical tubular reactor heated at 200 to 400 C., the said upper end containing a packing from a metal selected from the groups consisting of copper metal and an alloy containing a major proposition of copper, on which packing the cyclopentadiene can vaporise; the resulting monomer vapours are subsequently mixed with the vapours of a liquid which boils between and 360 C. and does not decomposewithin this temperature range and is inert towards the monomeric form and the dimeric form of the cyclodiene; the resulting vapour mixture is conveyed into a fractionating column and the pure monomer is withdrawn in the form of a distillate at the head of the column; the dimeric cyclodiene is injected into the reactor at the same rate as monomeric cyclodiene is withdrawn; the column is equipped with .a device which, on the one hand, when the boiling point of pure monomeric cyclodiene is exceeded causes a total reflux within the column and at the same time shuts off the supply of dimer to the reactor and, on the other hand, reinstates the supply of dimer and the withdrawal of distillate when the boiling temperature of the pure monomeric cyclodiene has been reestablished at th head of the column.

References Cited UNITED STATES PATENTS 2,801,270 7/1957 Nelson et a1 260--666 2,831,904 4/1958 Kreps 260-666 2,913,504 11/1959 Hillard et al 260666 2,933,539 4/1960 Hillard 260666 3,007,978 11/1961 Beach 260666 3,016,410 1/ 1962 Dick et a1 260-666 FOREIGN PATENTS 612,893 1 1/ 1948 Great Britain. 769,813 3/ 1957 Great Britain.

DELBERT E. GANTZ, Primary Examiner.

V. OKEEFE, Assistant Examiner. 

